The present invention relates generally protection of pipelines and pipeline operators, and in particular to an apparatus and method for embedded Alternating Current (AC) corrosion mitigation.
Overhead electrical transmission lines and pipelines often run in parallel in Right Of Ways (ROWs) due to limited land access. Electrical current can be induced onto the pipelines due to electro magnetic fields created by AC current in the overhead electrical transmission lines near the pipelines. The electrical current induced onto the pipeline is commonly referred to as AC interference. AC interference can create unsafe conditions (electrical shock hazards) for pipeline operators as well as cause a phenomenon called AC corrosion. Both the unsafe conditions and the AC corrosion are the effect of increasing AC voltage/current by induction/fault through the pipeline under the effect of AC interference.
Pipelines are often coated to reduce or prevent chemical and electro chemical corrosion. The coatings also act as electrical insulation and a well coated pipeline generally prevents or reduces leakage of current into surrounding media and allows increased accumulation of AC voltage/current within the pipeline. The increased accumulation of AC voltage/current increases problems caused by the AC voltage/current.
Newly-developed (highly efficient) coatings have increased the dielectric properties of pipelines. Pipelines coated with such coatings are even less electrically lossy to the media around them than pipelines with older and less efficient coatings. As a result, the possibility of increasing AC voltage/current on new pipelines with high efficiency coatings is often considerably higher than from pipelines with older coatings.
A known method for mitigation of the accumulation of AC voltage/current on pipelines is through the use of Direct Current (DC) decouplers and grounding systems as a combination. DC decouplers are basically capacitors including a dielectric material which allows current to pass through the dielectric material when the voltage rises above a certain range. The DC decouplers are also pass the AC current and stop the DC current, so the AC current will be transferred to the grounding system and the DC remain in the line. The DC decouplers include two conductors separated by the dielectric material. The dielectric could be air, glass, paper, a vacuum, a semiconductor, or a dielectric coating. The DC decouplers will hold the DC current inside the pipeline in order to cathodically protect the pipeline from external corrosion, and transfer the AC current to a grounding system. Another known method is to install zinc ribbon anodes along the pipeline section under the effect of AC interference. Unfortunately, these existing methods have not satisfactorily eliminated the dangers and damage cause by the AC voltage/current in pipelines.